EP1202552B1 - Méthode pour générer et détecter des filigranes - Google Patents

Méthode pour générer et détecter des filigranes Download PDF

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EP1202552B1
EP1202552B1 EP01309049A EP01309049A EP1202552B1 EP 1202552 B1 EP1202552 B1 EP 1202552B1 EP 01309049 A EP01309049 A EP 01309049A EP 01309049 A EP01309049 A EP 01309049A EP 1202552 B1 EP1202552 B1 EP 1202552B1
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basis
function
pattern
image
basis function
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EP1202552A3 (fr
EP1202552A2 (fr
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Peter Alleine Fletcher
Kieran Gerard Larkin
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Canon Inc
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Canon Inc
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T1/00—General purpose image data processing
    • G06T1/0021—Image watermarking
    • G06T1/005—Robust watermarking, e.g. average attack or collusion attack resistant
    • G06T1/0064—Geometric transfor invariant watermarking, e.g. affine transform invariant
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T1/00—General purpose image data processing
    • G06T1/0021—Image watermarking
    • G06T1/0028—Adaptive watermarking, e.g. Human Visual System [HVS]-based watermarking
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N1/32101—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N1/32144—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
    • H04N1/32149—Methods relating to embedding, encoding, decoding, detection or retrieval operations
    • H04N1/32154—Transform domain methods
    • H04N1/3216—Transform domain methods using Fourier transforms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N1/32101—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N1/32144—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
    • H04N1/32149—Methods relating to embedding, encoding, decoding, detection or retrieval operations
    • H04N1/32203—Spatial or amplitude domain methods
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N1/32101—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N1/32144—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
    • H04N1/32149—Methods relating to embedding, encoding, decoding, detection or retrieval operations
    • H04N1/32203—Spatial or amplitude domain methods
    • H04N1/32208—Spatial or amplitude domain methods involving changing the magnitude of selected pixels, e.g. overlay of information or super-imposition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
    • H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N1/32101—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N1/32144—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title embedded in the image data, i.e. enclosed or integrated in the image, e.g. watermark, super-imposed logo or stamp
    • H04N1/32149—Methods relating to embedding, encoding, decoding, detection or retrieval operations
    • H04N1/32203—Spatial or amplitude domain methods
    • H04N1/32251—Spatial or amplitude domain methods in multilevel data, e.g. greyscale or continuous tone data
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2201/00—General purpose image data processing
    • G06T2201/005—Image watermarking
    • G06T2201/0083—Image watermarking whereby only watermarked image required at decoder, e.g. source-based, blind, oblivious
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2201/00—General purpose image data processing
    • G06T2201/005—Image watermarking
    • G06T2201/0202—Image watermarking whereby the quality of watermarked images is measured; Measuring quality or performance of watermarking methods; Balancing between quality and robustness
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N2201/3201—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N2201/3225—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of data relating to an image, a page or a document
    • H04N2201/3233—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of data relating to an image, a page or a document of authentication information, e.g. digital signature, watermark
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
    • H04N2201/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
    • H04N2201/3201—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title
    • H04N2201/3269—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs
    • H04N2201/327—Display, printing, storage or transmission of additional information, e.g. ID code, date and time or title of machine readable codes or marks, e.g. bar codes or glyphs which are undetectable to the naked eye, e.g. embedded codes

Definitions

  • the present invention relates to the generation, embedding and detection of patterns in images, audio streams, video, and documents or surfaces of articles.
  • Such embedded patterns may be used for invisible watermarking, and/or for alignment information.
  • the present invention relates to embedded patterns that have scale and rotation invariant properties.
  • One technique used to identify the ownership of an image is to embed a pattern or patterns into the image, such that the embedded pattern is not visible to the naked eye of an observer. Such a pattern is called a watermark. The presence of the watermark can be detected in the copied image by the owner of the original image, thereby proving their ownership.
  • spectral method is an analysis of the Fourier magnitude peaks of the image with an embedded watermark.
  • correlation One of the most popular and effective methods for detecting patterns is correlation.
  • correlation, or matched filtering can be shown to be mathematically an optimal detection method.
  • correlation in two dimensions is not, in general, invariant with orientation or scaling.
  • correlation can only give well defined and easily distinguished correlation magnitude peaks if the underlying pattern has a broad Fourier magnitude distribution. This is a consequence of the uncertainty principle. Therefore, patterns with very sharp or constrained Fourier magnitudes, such as a narrow-bandpass function, are ill equipped for correlation purposes.
  • Rotation invariance in known systems is typically achieved by using circular symmetric patterns.
  • the correlation can be repeated many times with the test pattern at many different orientations, so that at least one correlation is close to the actual orientation.
  • Scale related problems are usually solved by repeated correlations at many different scales so that at least one correlation is close to the actual scale. Such methods are impractical, and as a consequence correlation seldom is used in cases when arbitrary rotation and/or scaling is present.
  • EP-A-1003324 discloses a system for embedding machine detectable multi-bit information within an image on a document where the hidden information may correlate for example with textual information printed on the document.
  • JP-A-2000-268178 discloses a method of separating a rotation parameter of a rotation scaled translation conversion using a Fourier-Mellin invariant.
  • a reference image and a pattern image are compared and the rotation, scaling and translation shift parameters determined from the two images are separated from one another using a Fourier-Mellin invariant.
  • US-A-6266452 discloses a method for registering a pattern image with a reference image.
  • the pattern image and the reference image differ from one another by a rotation-scale-translation transformation defined by a scale factor, a rotation factor and a translation vector.
  • a Fourier-Mellin invariant is used to perform image registration by isolating the rotations, scale and transformation parameters of the combined transformation between the reference image and the pattern image.
  • US-A-5257325 discloses an apparatus and method for electronically registering and lining ideal raster data to real raster data for subsequent processes such as inspection systems and image processing systems.
  • An electronic image recognition system receives ideal and real images in scrolling buffers wide enough to hold the width of the image and high enough to hold the difference in a skewed image. Each buffer has a selector to randomly access frames of image in the vertical direction.
  • WO-A-00/39955 discloses a method of adaptive content based embedding of a digital audio signal. Corresponding watermark extracting techniques are also disclosed. The watermark information is encrypted using an audio digest signal.
  • the original audio signal is divided into fixed frames lengths in the time domain. Echoes are embedded in the original audio signal to represent the watermark.
  • the watermark is generated by delaying and scaling the original audio signal and embedding it in the audio signal.
  • An embedding scheme is designed for each frame according to the properties in the frequency domain.
  • a multiple echo hopping module is used to embed and extract watermarks in the frame of the audio signal.
  • Altes R A "Signal Processing for Target Recognition in Biosonar" Neural Networks, Elsevier Science publishers, Barking, GB, vol. 8, no. 7, 1995, pages 1275-1295 , discloses a system for target recognition by association of echo features derived from time frequency or range-Doppler distribution and their projections as well as images derived from echoes observed in different positions.
  • Such an image can be obtained with a rotated wavelet (line segment) transform which is a generalisation of wavelet and radon transform.
  • the rotated wavelet transform permits recursive delay and some beam forming with a sparsely sampled synthetic aperture constructed with a moving multi beam sonar system.
  • the basis functions for the transform are rotated spaced-time transmission patterns similar to those used by echo locating dolphins.
  • an image processing apparatus for embedding a mark into an image in accordance with claim 21 and a data processing apparatus for embedding a mark into an audio stream in accordance with claim 33.
  • a memory medium storing a computer program to program a programmable apparatus in accordance with claim 41 and a signal carrying instructions for causing a programmable processing apparatus to perform a method in accordance with claim 50.
  • Equation (1) has some peculiar properties, such as an infinite number of periods in the range 0 ⁇ r ⁇ ⁇ , and the phase approaches - ⁇ as the radius tends to zero. The undesired effects of these properties can be largely avoided by removal of a central region below a threshold radius.
  • Fig. 1 shows a one-dimensional example of a simple oscillating homogeneous function having the form of Equation (1), for values 0.01 ⁇ x ⁇ 1.
  • the homogeneity condition can also be viewed as a self-similarity criterion.
  • Self-similar functions produce correlation magnitude peaks even when one of the correlated functions is rescaled.
  • Equation (7) represents a family of functions, which have a periodic radial structure.
  • the complex function ⁇ ⁇ ( r ) has negative values. Therefore, for the function ⁇ ⁇ ( r ) to be displayed, the values the function ⁇ ⁇ ( r ) have been normalised around a value of 127, with all values ranging from 0 to 255, with 0 representing black, 255 representing white, and intermediate levels representing levels of grey.
  • Equation (7) Functions of the form of Equation (7) have some useful orthogonality properties over an annular region, with the annular region defined by a maximum radius R 2 and the minimum radius R 1 .
  • 2 may be written as a sinc function as follows: I mn 2 ⁇ 4 ⁇ ⁇ 2 ⁇ sin 2 ⁇ 1 2 ⁇ ⁇ m - ⁇ n ⁇ ln R 2 / R 1 ⁇ m - ⁇ n 2
  • the above condition is an approximate orthogonality condition, useful for estimation purposes.
  • the ratio R 2 / R 1 is chosen to be of the order 2 to 4, so that ln( R 2 / R 1 ) ⁇ 1.
  • a scale and rotation invariant pattern g which has a circular harmonic phase defined by the parameter k , where parameter k is an integer.
  • the LRHF g mk is evaluated over a discrete image with a finite size, and where the pixel positions ( x,y ) only contain discrete integer values.
  • constraints are imposed on the allowable values for the parameters k and ⁇ m .
  • the radial and tangential frequencies are square additives.
  • the full 2D frequency is just the vector sum of the radial and tangential frequency vectors.
  • ⁇ ( ) is the generalised factorial (gamma) function.
  • LRHFs g mk having the form of Equation (13), have the following transform pair: r p ⁇ r i ⁇ m ⁇ e ik ⁇ ⁇ ⁇ mkp ⁇ q - p - 2 ⁇ q i ⁇ m ⁇ e ik ⁇
  • Correlation between pattern g mk and image ⁇ produces a 2 dimensional image with maximum values at positions where the image ⁇ best matches the pattern g mk .
  • G u v H u v
  • correlation can be implemented by Fourier transforming the image f and the pattern g to obtain Fourier transformed functions F and G , complex conjugating one of the Fourier transformed functions, say F, and then multiplying these two functions F * and G , before transforming back.
  • the effectiveness of the embedding and detection of pattern g mk in typical images depends on the cross-correlation of the original image p with the chosen pattern g mk being of low magnitude and widely dispersed. This is difficult to estimate however, generally, the cross-correlation part is very small compared to the auto-correlation part.
  • the heuristic argument for this is that LRHFs do not resemble features in typical images p .
  • the LRHFs proposed have both wide spatial support and wide spectral support.
  • Equation (33) the correlation between two LRHFs g mk ( r ) and g nl ( r ), being the second term in Equation (33).
  • phase cancellation is the classic condition for maximum correlation, although a purely linear phase component can exist and only indicates a shift in the two original functions.
  • the discrete image f ( x , y ) is typically further limited by only 8 bits of data per pixel, thus greyscale levels 0-255.
  • all the preceding analysis extends easily to the case where a real pattern ( g mk ) is embedded in an image p ( x,y ) and detected with a complex pattern g nl .
  • the main difference is a 2 times increase in the noise compared to the full complex correlation, or: R g mk ⁇ g nl ⁇ g mk ⁇ g nl 2
  • the maximum frequency q max is kept below the Nyquist frequency of the discrete image.
  • the maximum frequency q max is as defined in Equation (27), and determines the size of the 'hole' in the centre of the pattern.
  • the size of the image introduces a maximum pattern size.
  • the pattern is restricted to an annular region defined by radii R 1 and R 2 .
  • One form of enhanced correlation is to boost the high frequency components of the conventional correlation. This has the effect of changing the real exponent p in Equations (37) and (38) resulting in a correlation peak which resembles the delta function in the second part of Equation (38).
  • phase-only correlation is implemented by taking the Fourier correlation magnitude, expressed in Equation (37) for example, and setting it to unity. This ensures that only the phase terms contribute to the overall correlation peak. Again, the peak shape tends to resemble a delta function.
  • a variety of enhanced correlation processes which consist of intermediates between frequency-boosted correlation and phase-only correlation, are also possible and applicable to the correlation detection.
  • the ratio of the two radii R 1 and R 2 in the annulus determine the extremes of the possible scale variations before correlations fail completely.
  • the minimum scaling factor is R 1 / R 2 and the maximum is R 2 / R 1 .
  • the range of scale variation may be extended by performing the correlation upon a number of differently scaled versions of the watermarked image. This allows the overlap area to be improved in at least one of the correlations. So, for example a sequence of images rescaled by progressive factors of 2 would guarantee one of the images to fit the 50% overlap criterion (for ⁇ ⁇ 4), and hence give a strong correlation peak.
  • Fig. 4 shows a schematic diagram of a process 450 of watermarking an image 400 or document with a pattern 410, such as the real part of a LRHF g mk shown in Fig. 3A .
  • the pattern 410 which may be called a watermark, is simply added to the image 400 to form a watermarked image 420. If the image 400 is in colour, then the pattern 410 is added to the luminance part of a colour image 400. This allows the watermark to survive when the watermarked image is converted from colour to a greyscale representation.
  • the pattern 410 component in the watermarked image 420 is invisible or imperceptible to the human visual system under normal viewing conditions. This is done by multiplying the pattern 410 with a constant embedded factor 430, thereby adding a low intensity copy of the pattern 410 to the image 400.
  • a collection of patterns may also be added to the image 400.
  • Fig. 5 shows the sum of 6 shifted LRHFs, similar in form as those shown in Fig. 3A .
  • a scale is applied to their intensity, or the intensity of their sum in the case of a collection of patterns, so that their intensity is approximately of the range -5 to +5 (for example) to avoid wide intensity variation. It is noted that the intensities of the image shown in Fig. 5 has been amplified to the range 0-255 to more clearly show the patterns.
  • Fig. 6 shows the watermarked image formed by adding the watermark represented in Fig. 5 to a test image, in this case Lena.
  • the watermark is perceptible in regions having low intensity variation, such as region 501.
  • an adaptive scheme is used to reduce the level of the watermark in regions having low intensity variation and increase the level of the watermark in regions of high intensity variance.
  • the window function w n ( r, ⁇ ) is a slowly varying function relatively to the pattern function r p r i ⁇ m e ik ⁇ .
  • the window function w n ( r, ⁇ ) is used to remove or de-emphasise the high frequency central region of the pattern function r p r i ⁇ m e ik ⁇ .
  • the window function w n ( r, ⁇ ) is also used to reduce the pattern intensity in regions of an image to which it is applied, where the pattern would otherwise be highly visible, such as "flat" sky regions.
  • the de-emphasis window function w n ( r, ⁇ ) may be calculated by estimating the perceptual masking in various regions of the image.
  • An example measure of perceptual masking is local gradient magnitude of the luminance in the image.
  • Others include second partial derivatives of the luminance; local estimates of the "energy" or frequency content, local variance, and more sophisticated estimates of human visual system masking.
  • Fig. 7A shows a schematic diagram of an alternative process 750 of watermarking an image 700.
  • a perceptual mask 720 is formed from the image 700.
  • the pattern 710 with parameters k and m (or a combination of patterns) is then de-emphasised with the perceptual mask 720 by multiplying the pixel values of the perceptual mask 720 with corresponding pixel values of the pattern 710.
  • the resulting pattern is of the form of Equation (45). This de-emphasised pattern is added to the image 700 to for a watermarked image 730.
  • the pattern 710 component in the watermarked image 730 is invisible or imperceptible to the human visual system under normal viewing conditions. This is done by multiplying the pattern 710 with a constant embedded factor 740, thereby adding a low intensity copy of the pattern 710 to the image 700.
  • Fig. 7B shows the watermarked image formed by adding the watermark represented in Fig. 5 to the test image, using the process 750 shown in Fig. 7A .
  • the watermark that was perceptible in region 501 of Fig. 6 is no longer perceptible in a corresponding region 502.
  • the window function w n ( r , ⁇ ) can also contain other information, for example a constant phase (ie complex) factor.
  • a phase factor causes a constant phase offset to the pattern function r p r i ⁇ m e ik ⁇ .
  • this phase factor is made random, making every watermark unique, even when the same parameters ⁇ m and k are used. Such a watermark would be even harder to detect.
  • the de-emphasised pattern ⁇ k,m,n ( x , y ) may be added to the luminance part of the signal.
  • the de-emphasised pattern ⁇ k,m,n ( x , y ) may be added to the R, G, B, H, V, S, u, v etc channels of the colour image, or any combination thereof.
  • the watermark encodes information in the centre location ( x n , y n ) strength, relative phase, and parameters k(n) and ⁇ m(n) of each of the N basis patterns ⁇ .
  • the centre location ( x n , y n ) strength is not a robust carrier of information, as it can be easily attenuated, even accidentally, by any processing of the watermarked image.
  • Fig. 8 shows a schematic diagram of a process 800 of detecting a watermark in a watermarked image 810.
  • the watermarked image 810 is simply correlated with a complex pattern 820 having parameters k and ⁇ m , such as that shown in Figs. 3A and 3B , to form a result image 830.
  • the complex pattern 820 is present in the watermarked image 810, in particular the real part of a LRHF having parameters k and ⁇ m
  • the result image 830 will have correlation magnitude peak(s) at centre location(s) where that pattern 820 was embedded into the image.
  • the use of different parameters, say l and ⁇ n in the pattern 820 will result in no correlation magnitude peaks in the result image 830.
  • the process 800 of detection may be repeated for each of the basis patterns ⁇ .
  • the process 800 may also be used with watermarked images 810 where process 750 shown in Fig. 7A was used to embed the watermark 710 into the image 700, using de-emphasis of the watermark.
  • Fig. 9 shows a schematic diagram of an alternative process 900 of detecting a watermark in a watermarked image 910.
  • a perceptual mask 920 is formed from the watermarked image 910.
  • the watermarked image 910 is then emphasised with the perceptual mask 920 by dividing the pixel values of the watermarked image 910 by pixel values of corresponding pixel values of the perceptual mask 920.
  • This emphasised image 930 is correlated with the complex pattern 940 to for a result image 950.
  • Fig. 10A shows the magnitude image of the correlation of the correct LRHF g mk ( r ) with the watermarked image of Fig. 6 using process 800.
  • Fig. 10B shows the detail of the peak structure of one of the magnitude peaks of Fig. 10A .
  • Fig. 11A shows the magnitude image of the correlation of the correct LRHF g mk ( r ) with the watermarked image of Fig. 7B using process 900
  • Fig. 11B shows the detail of the peak structure of one of the magnitude peaks of Fig. 11A .
  • the magnitude peaks shown in Figs. 10B and 11B are very sharp and clear, whereas the background correlation is small. An improvement in the sharpness of the magnitude peaks is also visible in Fig. 11B .
  • the watermark process 750 using de-emphasis makes the pattern less perceptible
  • the watermark detection process 900 using emphasis improves detection by resulting in sharper magnitude peaks.
  • the magnitude peaks can only be detected by correlation with the known LRHF(s) used for embedding, or by an exhaustive search of correlation magnitude peaks by using the full range of parameters k and ⁇ m .
  • the exhaustive search can be expected to be many orders of magnitude slower than detection using the correct parameters k and ⁇ m , making the method difficult to attack.
  • Fig. 12 shows the watermarked image of Fig. 7B rotated by 20 degrees and increased in size by 20%. The image has also been cropped and a gamma correction power of 0.8 has been applied. These operations were performed on the 8-bit image data using linear interpolation.
  • Fig. 14 shows the detail of the peak structure of one of the magnitude peaks of Fig. 13 . There is some degradation of the peak structure compared to the magnitude peaks of Fig. 11B , but the correlation magnitude peaks are still well above the background noise level.
  • detection is relatively straightforward, in that the pixel containing the maximum modulus value is selected , and its coordinates define the centre of the embedded pattern.
  • a slightly more complex approach is used. If a detection image contains s peaks, those s peaks may be detected as follows:
  • the radius q is chosen depending upon the application. When alignment peaks are very well spaced, a large value for q , say 20 pixels, may be used. Peaks used to encode information may be much closer together, and a smaller value for q should be used.
  • the method is more difficult to defeat than known methods where the watermarks can be detected by analysing the Fourier magnitudes of an image. Detection of LRHF g mk ( r ) based watermarks requires many correlations, typically more than 1000, if the parameters ⁇ m and k of the LRHF g mk ( r ) are unknown.
  • LRHF is restricted to an annular region defined by radii R 1 and R 2 .
  • square or other shapes may also be used to restrict the patterns.
  • Fig. 16A shows the real part of an example a LRHF restricted within a sub-region having an trapezoidal shape. Even though the sub-region does not in itself have any rotational symmetry properties, nor is it strictly orthogonal, it is nevertheless detected effectively at any rotation angle by correlation with a full circular complex LRHF. Accordingly, either of process 800 or 900 shown in Figs. 8 and 9 respectively may be used to detect such a pattern having an arbitrary shape. The scaling and cropping invariant properties are similarly maintained.
  • Fig. 16B shows the intensity of a correlation magnitude peak as a result of correlating a square LRHF with a circular complex LRHF. This may be compared with the intensity of the correlation magnitude peak as a result of correlating the arbitrarily shaped LRHF shown in Fig. 16A with the circular complex LRHF, which is shown in Fig. 16C . It can be seen that a distinct peak is still formed which may be detected in the usual manner.
  • the magnitude peak shown in Fig. 16C tends to be elliptical rather than circular in the specific example, with the intensity of the sidelobes being about 30% of that of peak value.
  • Watermarks based on LRHFs are particularly suited for embedding alignment marks in images to allow reliable registration and alignment of an image of, or applied to the object.
  • alignment marks could take many forms.
  • three basis patterns ⁇ are added to the image, with the basis patterns ⁇ having centre locations ( x n , y n ) corresponding with the positions of three corners of a square of known size forming an 'L'-shape.
  • the basis patterns ⁇ may be embedded visibly or invisibly using process 450 or 750 set out above.
  • the detection of the possibly transformed centre locations ( x n ,y n )' of the alignment marks is performed by using method 800 or 900, shown in Figs. 8 and 9 respectively.
  • the translation may be estimated as follows:
  • a rotation angle may be estimated using the vector between the two detected centre locations ( x n ,y n )' or peaks which are furthest apart. Similarly, a total scaling factor may be estimated using the distance between these two peaks. A shear factor may be estimated by measuring the angle between the three peaks. A change in aspect ratio may be estimated by measuring the difference in the length of the horizontal side and the vertical side of the "L" shape formed by the three peaks. The middle point of the 'L' shape may be used to define the coordinate system origin of the alignment marks.
  • the four parameters completely define a linear transformation. Reflections and non-linear transformations such as warping or removal of image columns or rows can not be detected and therefore can not be inverted.
  • the linear transformation may be inverted to restore the watermarked image to its original size and orientation.
  • Scaling and rotation may be performed by a variety of resampling algorithms. Typically a high quality resampling using bi-cubic interpolation, Fourier interpolation, or even a non-linear resampling scheme may be used.
  • an alternative watermarking or steganographic method may be utilised to extract further information from the image.
  • the registration patterns are used in conjuction with any other watermarking technique.
  • the registration is performed before reading the embedded watermark.
  • Registration may include focusing because the correlation magnitude peaks provide a nice smooth variation in magnitude with respect to changes in the focus of imaging systems. Focus can be estimated by correlation peak width. An advantage of a width based measure of focus is that it is normalised and does not depend upon the absolute peak level.
  • Registration may further include aspect ratio correction and shearing to some extent, due to the strength of the correlation magnitude peaks.
  • Process 450 or 750 shown in Fig. 4 and 7 respectively, may be used to embed the pattern into an image.
  • the one dimensional pattern may be detected using process 800 or 900, shown in Figs. 8 and 9 respectively, to detect the centre line position of a pattern, if the correct parameter ⁇ m is known.
  • a two-dimensional complex pattern having the form of Equation (13) is used as the pattern 820 in process 800, with the two-dimensional complex pattern having the same parameter ⁇ m , but zero spiral parameter k.
  • the detection is unaffected by shear or anamorphic magnifications.
  • the watermark encodes information in the centre location ( x n ,y n ) strength, phase, and parameters k(n) and ⁇ m(n) of each of the N basis patterns ⁇ .
  • the location ( x n ,y n ) of each peak could store several bits of data. More sophisticated methods may also be used such as described below. Detection of the stored data requires that the peak and its position be identified reliably. This process may entail some error correcting or data redundancy scheme.
  • each basis pattern ⁇ centred on a pixel in a 64x64 square grid in the image which is used for watermarking.
  • each grid position is preferably separated by 7 pixels, thus the template grid pattern covers a region of 448x448 pixels in the candidate image, which is small enough to embed in all but the smallest images.
  • This technique uses three points on a regular grid to provide information on the pattern orientation and scaling, a point to encode image length, and subsequent points to encode bits of information.
  • each row and column position of the marks in the original grid may be derived from the detected position of each basis embedded in the watermarked image.
  • the first three points define the corners of the embedding grid.
  • a different basis pattern ⁇ defines each point, thus they may be detected in order and their relative positions used to establish the orientation and scaling of the grid in the watermarked image, and sufficiently small shear or anamorphic scaling changes.
  • a linear transformation may be derived from the coordinates of the watermarked image to that of the original 64 point by 64 point grid.
  • the fourth point in the sequence of detected bases is used to encode the length of the encoded message in bits. By assigning numbers from 0 to 4095 to each grid position, the fourth point may indicate a message of any length from 0 to 4095 bits.
  • Subsequent points encode the bits of the message by concatenating the bits representing the row and column address of each point.
  • each row or column address codes exactly 64 (2 6 ) separate values.
  • each point on the 64x64 grid encodes up to 12 bits.
  • Encryption may be performed on the bitstream to hide information from persons not holding the appropriate keys.
  • Checksums may be added to the bitstream to provide verification of the detected watermark, and also as an aid in locating information-containing watermark patterns.
  • Error-correcting codes may be added to the bitstream to increase the robustness of the encoded bitstream, albeit with the requirement of embedding more basis patterns ⁇ in the original watermark, perhaps making the mark more visible.
  • multiple basis patterns ⁇ may be added together at the same position and the sum of their detection magnitude peaks used during detection.
  • each detection peak alone may be too small to measure, but the summation of the amplitude of all detection images will combine to produce a very well-defined peak. Only by knowing a large fraction of the multiple bases can the detection peak, and hence the basis for watermarking, be found.
  • the process of embedding and detecting rotation and scale invariant bases has several properties, which provide the means to embed a substantial amount of information in an image watermark and recover it with great reliability. These properties include:
  • the amplitude peaks recovered from a watermarked image are extremely sharp and well localized, typically within 1-2 pixels. Thus their embedded position in the original image can be recovered with a great degree of accuracy.
  • Each watermarking basis pattern ⁇ is orthogonal to all other bases having different parameters k and ⁇ m . Thus, if many different bases patterns ⁇ are used in the watermark, a peak for each basis may be recovered almost independently of all other bases patterns ⁇ .
  • a single basis pattern ⁇ is used to embed a watermark, the magnitude peaks in the detected image will all be of identical complex phase. If multiple basis patterns ⁇ are used which differ only in complex phase, i.e. each basis pattern ⁇ is multiplied by a different complex constant of unit modulus, then the relative phase of all detected magnitude peaks will be preserved. In the best case, a single detected point may be used to determine the base phase, and the phase of subsequent magnitude peaks in the result image will retain their relative relationship to this base point.
  • the sharpness and amplitude of detection magnitude peaks is not substantially affected by any rotation or scaling transformations applied to the image, although the position of the magnitude peaks themselves will be rotated and scaled with the watermarked image. Thus, any rotation or scaling can be detected and corrected for by using the position of alignment points.
  • shearing or anamorphic (aspect ratio) changes may also be detected and taken into account, thus the method is applicable to arbitrary linear transformations as long as the shear, scaling or anamorphic component is small enough.
  • a watermark allows a code to be embedded into an image. Such a code will remain with the image even if the header and other metadata of the image file are removed. This allows the code to remain strongly attached to the actual image itself.
  • the code may be usefully employed to define the address or location of the original metadata related to the image.
  • the metadata may contain owner identification, camera settings, geographical location, details of the subjects in the image, or any number of pieces of other information.
  • Image metadata may be stored on the same device as the image, or on a server connected by a network, or even a server owned by a third party on the Internet.
  • a watermark can also embed a copyright owner's information into an image.
  • the copyright information will be difficult to detect or remove by anyone who does not have knowledge of the parameters used to define the embedded patterns. Without the embedded pattern parameters it is necessary to search a large number of possible configurations before correlation peaks may be detected. The difficulty in searching may be sufficient to dissuade attacks upon this copyright marking method.
  • the processes 450, 750, 800 and 900 can be implemented on a system 200 shown in Fig. 15 .
  • one or more of the processes 450, 750, 800 and 900 may be implemented as software executing within the system 200, where the processes 450, 750, 800 and 900 are effected by instructions in the software that are carried out by the system 200.
  • the software may be stored in a computer readable medium, including the storage devices described below, for example.
  • the software is loaded into the system 200 from the computer readable medium, and then executed by the system 200.
  • a computer readable medium having such software or computer program recorded on it is a computer program product.
  • the use of the computer program product in the system 200 preferably effects an advantageous apparatus for watermarking, watermark detection or registration.
  • the pattern embedding and detecting processes 450, 750, 800 and 900 may be included as a plug-in module for commercially available software packages.
  • packages which are used for the manipulation and editing of digital image files would benefit by the addition of the pattern embedding and detection software.
  • the embedding and/or the detection of the watermarks may be operated as a service by a third party.
  • the images may be conveyed by a digital network for embedding and then returned to the owner with the hidden mark.
  • an image thought to contain a mark may be submitted to the third party operator for detection of marks with specified parameters.
  • the system 200 may, for example, be a general-purpose computer, a digital camera, a video camera, a scanner or a photocopier.
  • the system 200 comprises a computer module 201, output device(s) 215 and input devices such as controls 202 and digital capture device 203.
  • the digital capture device 203 may be an image sensor, such a two-dimensional CCD array.
  • the computer module 201 typically includes at least one processor unit 205, a memory unit 206, for example formed from semiconductor random access memory (RAM) and read only memory (ROM), input/output (I/O) interface(s) and a storage device 209.
  • the components 205 to 213 of the computer module 201 typically communicate via an interconnected bus 204 and in a manner which results in a conventional mode of operation of the computer system 200 known to those in the relevant art
  • the output device 215 includes a display device.
  • a printer may also be provided.
  • the controls 202 include a keyboard and a mouse.
  • the storage device 209 typically includes a hard disk drive, a floppy disk drive and a CD-ROM drive.
  • the application program is resident on the storage device 209, and read and controlled in its execution by the processor 205. Intermediate storage of the program may be accomplished using the semiconductor memory 206, possibly in concert with the storage device 209.
  • the application program may be supplied to the user encoded on a CD-ROM or floppy disk and read via a CD-ROM drive or floppy disk drive 211, or alternatively may be read by the user from a network (not illustrated).
  • the software can also be loaded into the computer system 200 from other computer readable medium including magnetic tape, a ROM or integrated circuit, a magneto-optical disk, a radio or infra-red transmission channel between the computer module 201 and another device, a computer readable card such as a PCMCIA card, and the Internet and Intranets including e-mail transmissions and information recorded on websites and the like.
  • computer readable medium including magnetic tape, a ROM or integrated circuit, a magneto-optical disk, a radio or infra-red transmission channel between the computer module 201 and another device, a computer readable card such as a PCMCIA card, and the Internet and Intranets including e-mail transmissions and information recorded on websites and the like.
  • the system 200 is a digital camera or video camera
  • the image(s) and/or the watermarked image(s) may be stored onto the storage device 209 or communicated to another device (not illustrated).
  • One or more of the processes 450, 750, 800 and 900 may alternatively be implemented in dedicated hardware such as one or more integrated circuits performing the functions or sub functions of those processes 450, 750, 800 and 900.
  • dedicated hardware may include graphic processors, digital signal processors, or one or more microprocessors and associated memories.
  • images may be obtained by the system 200 using the digital capture device(s) 202 or through the storage device 209.
  • Watermarked images may be displayed, printed, stored or communicated to other devices.
  • watermarked images may be obtained by the system 200 using the digital capture device(s) 202 or through the storage device 209.
  • the watermarked image is displayed, printed or stored as a greyscale image on a medium which has a finite dynamic range and resolution, such as a bitmap file, liquid crystal display or a laser-printer output, the watermarked image is converted to a quantised facsimile or a halftone representation.
  • a medium which has a finite dynamic range and resolution, such as a bitmap file, liquid crystal display or a laser-printer output
  • Audio signals whether digital or (high quality) analogue may have very low level patterns or signals added with very little differences being perceptible. If the signal length is long enough, then a strong correlation peak is obtainable provided the pattern parameters are known. In this way information (copyright or otherwise) may be embedded in the audio signal.
  • the embedding device which may be software or hardware, may be located near the input of an audio capture device, such as a microphone. Alternatively the embedding process may take place near the output device of an audio production system. In this case the embedded patterns would be optimised for the final output medium, such as Compact Disc or Digital Audio Tape. The patterns would survive and still be detectable after sophisticated watermark attacks such as pitch changing and resampling because of the scale invariant property.
  • the correlation is performed optically through the use of spatial light modulators.

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Claims (50)

  1. Procédé d'incorporation d'une marque dans une image (400 ; 700), ledit procédé comprenant l'étape :
    de conservation d'un motif de base ; et
    d'ajout dudit motif de base à ladite image (400 ; 700) dans le domaine spatial à une pluralité de décalages spatiaux différents pour former une image filigranée (420 ; 730), ledit motif de base étant obtenu à partir d'une fonction de base, caractérisé en ce que ladite fonction de base est définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version de ladite fonction de base ayant subi une mise à l'échelle et une rotation, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  2. Procédé selon la revendication 1, dans lequel ledit motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  3. Procédé selon la revendication 1, dans lequel ladite fonction de base est une fonction g(r,θ) définie de façon que : g r θ ⊗ g ⁢ a . r , θ + φ = c . g r θ ⊗ g r θ
    Figure imgb0107
    où r est une distance de déplacement, θ et φ sont des angles, a est un nombre réel positif et c est ladite constante multiplicative complexe qui ne dépend ni de ladite distance r de déplacement ni dudit angle θ.
  4. Procédé selon la revendication 1, dans lequel ladite fonction de base est une fonction g(r,θ) définie en outre de façon que : g r θ ⊗ ℵ g ⁢ a . r , θ + φ = g r θ ⊗ ℵ c . g r θ
    Figure imgb0108
    où
    Figure imgb0109
    définit une composante réelle ou imaginaire, r est une distance de déplacement, θ et φ sont des angles, a est un nombre réel positif et c est ladite constante multiplicative complexe qui ne dépend ni de ladite distance r de déplacement ni dudit angle θ.
  5. Procédé selon la revendication 1, dans lequel ladite fonction de base est de la forme : g pmk r θ = r i ⁢ α m + p e ikθ ,
    Figure imgb0110
    avec k, p et α m qui sont des paramètres de ladite fonction de base.
  6. Procédé selon la revendication 1, dans lequel ledit motif de base est de la forme : g pmkn r θ = ℜ w n r θ . r i ⁢ α m + p e ikθ ,
    Figure imgb0111
    avec k, p et α m qui sont des paramètres de ladite fonction de base, et wn (r,θ) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée à ladite image (400 ; 700) au niveau de ladite pluralité de décalages différents.
  7. Procédé selon la revendication 6, dans lequel ladite fonction de fenêtre wn(r,θ) enlève ou désaccentue une région centrale de ladite fonction de base ayant des fréquences au-dessus d'une fréquence prédéterminée.
  8. Procédé selon la revendication 6, dans lequel ladite fonction de fenêtre wn(r,θ) désaccentue des régions de ladite fonction de base correspondant à des régions de ladite image (400 ; 700) ayant une faible variation de signal.
  9. Procédé selon la revendication 6, dans lequel ladite fonction de fenêtre wn(r,θ) contient un facteur de phase constant.
  10. Procédé selon la revendication 5, dans lequel on ajoute au moins un premier et un second motif de base à ladite image (400 ; 700), lesdits premier et second motifs de base étant formés à partir, respectivement, d'une première et d'une seconde fonction de base, et avec au moins un paramètre k ou α m de ladite première fonction de base qui est différent de celui de ladite seconde fonction de base.
  11. Procédé selon la revendication 5, comprenant l'étape initiale supplémentaire de codage d'information en au moins l'un desdits paramètres, dudit décalage, d'une amplitude ou d'une phase relative ajouté audit motif de base.
  12. Procédé selon la revendication 1, dans lequel ledit motif de base est obtenu à partir de la composante réelle de ladite fonction de base, ladite fonction de base étant de la forme : s l , m x y = xʹ i ⁢ α l + p x ⁢ yʹ i ⁢ α m + p y ,
    Figure imgb0112
    où px, py, αl et α m sont des paramètres de ladite fonction de base, et x' et y' sont des coordonnées prédéterminées qui ont subi une rotation par rapport aux coordonnées cartésiennes x et y.
  13. Procédé d'incorporation d'une marque dans un flux audio, ledit procédé comprenant l'étape :
    de conservation d'un motif de base ; et
    d'ajout dudit motif de base audit flux audio dans le domaine temporel à une pluralité de décalages temporels différents pour former un flux audio filigrané, ledit motif de base étant obtenu à partir d'une fonction de base, caractérisé en ce que ladite fonction de base est définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version mise à l'échelle de ladite fonction de base, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  14. Procédé selon la revendication 13, dans lequel ledit motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  15. Procédé selon la revendication 13, dans lequel ladite fonction de base est une fonction g(t) définie de façon que : g t ⊗ g a . t = c . g t ⊗ g t
    Figure imgb0113
    où t est un temps de déplacement, a est un nombre réel positif, et c est une constante multiplicative complexe qui ne dépend pas dudit temps t de déplacement.
  16. Procédé selon la revendication 13, dans lequel ladite fonction de base est une fonction g(t) définie de façon que : g t ⊗ ℵ g a . t = g t ⊗ ℵ c . g t
    Figure imgb0114
    où
    Figure imgb0115
    définit une composante réelle ou imaginaire, t est un temps de déplacement, a est un nombre réel positif et c est une constante multiplicative complexe qui ne dépend pas dudit temps t de déplacement.
  17. Procédé selon la revendication 13, dans lequel ladite fonction de base est de la forme : g pmn t = t i ⁢ α m + p ,
    Figure imgb0116
    avec p et α m qui sont des paramètres de ladite fonction de base.
  18. Procédé selon la revendication 13, dans lequel ledit motif de base est de la forme : g pmn t = ℜ w n t . t i ⁢ α m + p ,
    Figure imgb0117
    avec p et α m qui sont des paramètres de ladite fonction de base, et wn(t) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée audit flux audio au niveau de ladite pluralité de décalages différents.
  19. Procédé selon la revendication 18, dans lequel ladite fonction de fenêtre wn (t) enlève ou désaccentue une région de ladite fonction de base ayant des fréquences au-dessus d'une fréquence prédéterminée.
  20. Procédé selon la revendication 18, dans lequel ladite fonction de fenêtre wn(t) désaccentue des régions de ladite fonction de base correspondant à des régions dudit flux audio ayant une faible variation de signal.
  21. Appareil de traitement d'image destiné à incorporer une marque dans une image (400 ; 700), ledit appareil comprenant :
    un moyen (206, 209) de mémorisation mémorisant un motif de base ; et
    un moyen (205) destiné à ajouter ledit motif de base à ladite image (400 ; 700) dans le domaine spatial à une pluralité de décalages spatiaux différents pour former une image filigranée (420 ; 730), ledit motif de base étant obtenu à partir d'une fonction de base, caractérisé en ce que ladite fonction de base est définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version de ladite fonction de base ayant subi une mise à l'échelle et une rotation, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  22. Appareil selon la revendication 21, dans lequel ledit motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  23. Appareil selon la revendication 21, dans lequel ladite fonction de base est une fonction g(r,θ) définie de façon que : g r θ ⊗ g ⁢ a . r , θ + φ = c . g r θ ⊗ g r θ
    Figure imgb0118
    où r est une distance de déplacement, θ et φ sont des angles, a est un nombre réel positif et c est ladite constante multiplicative complexe qui ne dépend ni de ladite distance r de déplacement ni dudit angle θ.
  24. Appareil selon la revendication 21, dans lequel ladite fonction de base est une fonction g(r,θ) définie en outre de façon que : g r θ ⊗ ℵ g ⁢ a . r , θ + φ = g r θ ⊗ ℵ c . g r θ
    Figure imgb0119
    où
    Figure imgb0120
    définit une composante réelle ou imaginaire, r est une distance de déplacement, θ et φ sont des angles, a est un nombre réel positif et c est ladite constante multiplicative complexe qui ne dépend ni de ladite distance r de déplacement ni dudit angle θ.
  25. Appareil selon la revendication 21, dans lequel ladite fonction de base est de la forme : g pmk r θ = r i ⁢ α m + p e ikθ ,
    Figure imgb0121
    avec k, p et α m qui sont des paramètres de ladite fonction de base.
  26. Appareil selon la revendication 21, dans lequel ledit motif de base est de la forme : g pmkn r θ = ℜ w n r θ . r i ⁢ α m + p e ikθ
    Figure imgb0122
    avec k, p et α m qui sont des paramètres de ladite fonction de base, et wn (r,θ) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée à ladite image (400 ; 700) au niveau de ladite pluralité de décalages différents.
  27. Appareil selon la revendication 26, dans lequel ladite fonction de fenêtre wn (r,θ) enlève ou désaccentue une région centrale de ladite fonction de base ayant des fréquences au-dessus d'une fréquence prédéterminée.
  28. Appareil selon la revendication 26, dans lequel ladite fonction de fenêtre wn (r,θ) désaccentue des régions de ladite fonction de base correspondant à des régions de ladite image (400 ; 700) ayant une faible variation de signal.
  29. Appareil selon la revendication 26, dans lequel ladite fonction de fenêtre wn (r,θ) contient un facteur de phase constant.
  30. Appareil selon la revendication 25, dans lequel on ajoute au moins un premier et un second motif de base à ladite image (400 ; 700), lesdits premier et second motifs de base étant formés à partir, respectivement, d'une première et d'une seconde fonction de base, et avec au moins un paramètre k ou α m de ladite première fonction de base qui est différent de celui de ladite seconde fonction de base.
  31. Appareil selon la revendication 25, comprenant en outre un moyen destiné à coder de l'information en au moins l'un desdits paramètres, dudit décalage, d'une amplitude ou d'une phase relative, ajouté audit motif de base.
  32. Appareil selon la revendication 21, dans lequel ledit motif de base est obtenu à partir de la composante réelle de ladite fonction de base, ladite fonction de base étant de la forme : s l , m x y = xʹ i ⁢ α l + p x ⁢ yʹ i ⁢ α m + p y ,
    Figure imgb0123
    où px, py, αl et α m sont des paramètres de ladite fonction de base, et x' et y' sont des coordonnées prédéterminées qui ont subi une rotation par rapport aux coordonnées cartésiennes x et y.
  33. Appareil de traitement de données destiné à incorporer une marque dans un flux audio, ledit appareil comprenant :
    un moyen (206, 209) de mémorisation mémorisant un motif de base ; et
    un moyen (205) destiné à ajouter ledit motif de base audit flux audio dans le domaine temporel à une pluralité de décalages temporels différents pour former un flux audio filigrané, ledit motif de base étant obtenu à partir d'une fonction de base, caractérisé en ce que ladite fonction de base est définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version mise à l'échelle de ladite fonction de base, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  34. Appareil selon la revendication 33, dans lequel ledit motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  35. Appareil selon la revendication 33, dans lequel ladite fonction de base est une fonction g(t) définie de façon que : g t ⊗ g a . t = c . g t ⊗ g t
    Figure imgb0124
    où t est un temps de déplacement, a est un nombre réel positif, et c est une constante multiplicative complexe qui ne dépend pas dudit temps t de déplacement.
  36. Appareil selon la revendication 33, dans lequel ladite fonction de base est une fonction g(t) définie de façon que : g t ⊗ ℵ g a . t = g t ⊗ ℵ c . g t
    Figure imgb0125
    où
    Figure imgb0126
    définit une composante réelle ou imaginaire, t est un temps de déplacement, a est un nombre réel positif et c est une constante multiplicative complexe qui ne dépend pas dudit temps t de déplacement.
  37. Appareil selon la revendication 33, dans lequel ladite fonction de base est de la forme : g pm t = t i ⁢ α m + p ,
    Figure imgb0127
    avec p et α m qui sont des paramètres de ladite fonction de base.
  38. Appareil selon la revendication 33, dans lequel ledit motif de base est de la forme : g pmn t = ℜ w n t . t i ⁢ α m + p ,
    Figure imgb0128
    avec p et α m qui sont des paramètres de ladite fonction de base, et wn (t) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée audit flux audio au niveau de ladite pluralité de décalages différents.
  39. Appareil selon la revendication 38, dans lequel ladite fonction de fenêtre wn (t) enlève ou désaccentue une région de ladite fonction de base ayant des fréquences au-dessus d'une fréquence prédéterminée.
  40. Appareil selon la revendication 38, dans lequel ladite fonction de fenêtre wn (t) désaccentue des régions de ladite fonction de base correspondant à des régions dudit flux audio ayant une faible variation de signal.
  41. Support de mémorisation mémorisant un programme d'ordinateur pour programmer un appareil programmable de traitement pour qu'il soit utilisable pour mettre en oeuvre un procédé selon au moins l'une des revendications 1 à 20.
  42. Image marquée (420 ; 730) comprenant :
    une image d'origine (400 ; 700) ; et
    un motif de base ajouté à ladite image d'origine (400 ; 700) dans le domaine spatial à une pluralité de décalages spatiaux différents pour former ladite image filigranée (420 ; 730), caractérisée en ce que ledit motif de base est obtenu à partir d'une fonction de base, ladite fonction de base étant définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version de ladite fonction de base ayant subi une mise à l'échelle et une rotation, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  43. Image (420 ; 730) selon la revendication 42, dans laquelle ledit au moins un motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  44. Image (420 ; 730) selon la revendication 42, dans laquelle ladite fonction de base est de la forme : g pmk r θ = r i ⁢ α m + p e ikθ ,
    Figure imgb0129
    avec k, p et α m qui sont des paramètres de ladite fonction de base.
  45. Image (420 ; 730) selon la revendication 42, dans laquelle ledit motif de base est de la forme : g pmkn r θ = ℜ w n r θ . r i ⁢ α m + p e ikθ ,
    Figure imgb0130
    avec k, p et α m qui sont des paramètres de ladite fonction de base, et wn (r,θ) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée à ladite image (400 ; 700) au niveau de ladite pluralité de décalages différents.
  46. Flux audio comprenant :
    un flux audio d'origine ; et
    un motif de base ajouté audit flux audio dans le domaine temporel à une pluralité de décalages temporels différents pour former un flux audio filigrané, caractérisé en ce que ledit motif de base est obtenu à partir d'une fonction de base, ladite fonction de base étant définie de façon que ladite fonction de base, lorsqu'elle est corrélée avec une version mise à l'échelle de ladite fonction de base, est pratiquement égale à l'autocorrélation de ladite fonction multipliée par une constante multiplicative complexe.
  47. Flux audio selon la revendication 46, dans lequel ledit motif de base est une fonction réelle formée pratiquement à partir de ladite fonction de base.
  48. Flux audio selon la revendication 46, dans lequel ladite fonction de base est de la forme : g pm t = t i ⁢ α m + p ,
    Figure imgb0131
    avec p et α m qui sont des paramètres de ladite fonction de base.
  49. Flux audio selon la revendication 48, dans lequel ledit motif de base est de la forme : g pmn t = ℜ w n t . t i ⁢ α m + p ,
    Figure imgb0132
    avec p et α m qui sont des paramètres de ladite fonction de base, et wn (t) est une fonction de fenêtre, dans laquelle une composante réelle dudit motif de base est ajoutée audit flux audio au niveau de ladite pluralité de décalages différents.
  50. Signal transportant des instructions pour faire qu'un appareil programmable de traitement soit utilisable pour mettre en oeuvre un procédé selon au moins l'une des revendications 1 à 20.
EP01309049A 2000-10-27 2001-10-25 Méthode pour générer et détecter des filigranes Expired - Lifetime EP1202552B1 (fr)

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